Image removal



United States Patent 3,154,414 IMAGE REMOVAL Vsevoiod Tulagin, St. Paul,George H. Kalb, West St. Paul, and Donald K. Meyer, St. Paul, Minn,assignors to Minnesota Mining and Manufacturing Company, St. Paul,Minn., a corporation of Delaware No Drawing. Filed Apr. 18, 1960, Ser.No. 22,670 6 Claims. (Cl. 96-4) This invention relates to a new anduseful method for removing latent images from photoconductive sheetmaterials and restoring them to a dark adapted state.

Successive production of latent images on a photoconductive sheetmaterial is necessary in the preparation of colored reproductions byelectrolytic deposition of colored materials on the photoconductor sheetmaterial.

It is an object of this invention to make possible the preparation of aplurality of successive images on a photoconductive material in asimple, relatively fast, and convenient manner.

In the production of the images on a photoconductive sheet material, thephotoconductive material is selectively exposed to a light source of thevisible spectrum so that certain areas are rendered conductive afterexposure. This retained conductivity makes possible the subsequentproduction of the images by electrolytic means. Where two or moresuccessive images are to be applied the photoconductive sheet materialmust be restored to a dark adapted state before being re-exposed.Heretofore, photoconductive sheet materials have been restored to darkadapted state by heating the photoconductive sheet material at anelevated temperature or by storage in the dark for an extended period oftime.

It has noW been discovered that the removal of the latent image andrestoration of the photoconductive material to a dark adapted state isgreatly accelerated if the photoconductive sheet material is heated byplacing it in contact with hot water. In this manner a photoconductivesheet can be uniformly dark adapted in the matter of a few seconds byimmersion in hot water. Generally speaking, the water should be heatedto at least 100 F. (preferably about 140 F.) and remain in contact withthe photoconductor over a period of 10 to 60 seconds.

Photoconductor sheet materials of the type contemplated by thisinvention are prepared as follows:

A Waring Blendor mixer is employed to thoroughly blend the followingingredients over a period of minutes:

Methyl-isobutyl ketone -Q 139 Zinc oxide (U.S.P. 12) having a particlesize of less M than 40 microns 252 Binder [30% toluene solution ofbutadiene (30 parts by weight) and styrene (70 parts by weight)copolyrner] 210 sensitizing dyes are then added to the blend as 0.5%methanol solutions in order to dye-sensitize the photoconductor sheet asfollows:

1 Color Index," 2d ed., Chorley & Pickersgill Ltd., Leeds (1956) Afterbeing blended for an additional five minutes'and filtered through acoarse sintered glass filter, the blend was coated with a doctor bladecoater onto an aluminum sheet (3 mil) to a wet thickness of .006 inch.

When dry and fully dark adapted, this sheet was used to producereproductions and had high response spectral bands at 460-465 mu, 560 muand 660 mu.

Because of their flexibility, durability, and resistance to creaseformation, photoconductor sheet backings prepared by vapor deposition ofa metal, such as aluminum, on a paper or plastic backing are especiallyuseful. Polyethylene terephthalate films (5 mil) are preferred.

An illustrative procedure employed to prepare reproductions by theelectrolytic decomposition on the surface of a zinc oxide photoconductorsheet prepared as described above and to restore the photoconductor to adark adapted state is as follows:

(1) The negative electrode from a direct current power supply isattached to the aluminum backing of the photoconductor sheet.

(2) The photoconductor sheet retained in a developer tray is exposeduniformly to a white light source by projecting an image on thephotoconductor sheet with the projector having a low F stop projectionrange and a 500 watt tungsten projection lamp as the light source,thereby rendering the sheet conductive. Relative hu- Patented Oct. 27,1964 midity of the atmosphere in the work area is maintained at lessthan 40 percent.

(3) An electrode attached to the positive terminal of the direct currentpower supply is placed in the developer tray.

(4) A solution of Alcian Blue 8GN (5 g.) which is described in TheChemistry of Synthetic Dyes, by K. Venkataraman, Academic Press Inc.,New York, NY. (1952), dissolved in water (100 ml.) is added to thedeveloper tray.

(5) After a total lapse of time of about 20 seconds after exposure, a 30volt electrical current is then passed through the photoconductor andthe solution for a period of seconds.

(6) The solution is removed from the developer tray and thephotoconductor sheet is Washed with water heated to 140 F. for a periodof seconds to restore the photoconductor to a dark adapted state and thesheet is then dried by placing it under a stream of air. The resultingsheet had been rendered blue-green by the deposited dye.

(7) The sheet was then selectively exposed to a photographic image andtitanium dioxide deposited on the exposed areas by repeating steps 3 to5 above, using as the solution a suspension of titanium dioxide in adilute aqueous solution of the thiuronium salt prepared by reacting Ntetradecyl p-chloromethylbenzenesulfonamide and N,N,N,N-tetramethylthiourea. The titanium dioxide is deposited on the conductive areas ofthe photoconductor-cathode, which are areas selectively exposed to thephotographic image, concurrently with the decomposition of thiuroniumsalt, resulting in a positive bluegreen print.

We claim:

1. A process for restoring a photoconductor electrolytically developablesheet material having only latent conductivity images thereon to itsdark adapted state and for washing the surface thereof which comprisescontacting an organic photoconductor bonded to an electricallyconductive carrier with liquid water heated to at least 100 F. andcooling the heated photoconductor to ambient temperature.

2. A process for restoring a photoconductor electrolytically developablesheet material having only latent conductivity images thereon to itsdark adapted state and for washing the surface thereof which comprisescontacting an organic photoconductor bonded to an electricallyconductive carrier with liquid water heated to at least 100 F., dryingthe heated photoconductor and cooling the dry photoconductor to ambienttemperature.

3. A process for restoring an electrolytically developable zinc oxidephotoconductor sheet material having only latent conductivity imagesthereon to its dark adapted state and for washing the surface thereofwhich comprises contacting a zinc oxide photoconductor bonded to anelectrically conductive carrier liquid with water heated to at least F.and cooling the heated zinc oxide to ambient temperature.

4. A process for restoring an electrolytically developable zinc oxidephotoconductor sheet material having only latent conductivity imagesthereon to its dark adapted state and for Washing the surface thereofwhich comprises contacting a Zinc oxide photoconductor bonded to anelectrically conductive carrier liquid with water heated to at least 100F., drying the heated zinc oxide and cooling the dry zinc oxide toambient temperature.

5. A process for dark adapting and washing a zinc oxide photoconductorsheet material which comprises contacting a zinc oxide photoconductorbonded to an electrically conductive carrier with liquid water heated toat least 100 F. and cooling the heated zinc oxide to ambienttemperature, said steps being conducted under dark conditions.

6. A process for dark adapting and washing a zinc oxide photoconductorsheet material which comprises contacting a zinc oxide photoconductorbonded to an electrically conductive carrier with liquid water heated toat least 100 F., drying the heated zinc oxide and cooling the dry zincoxide to ambient temperature, said steps being conducted under darkconditions.

References Cited in the file of this patent UNITED STATES PATENTS2,286,744 Leatherman June 16, 1942 2,863,767 Vyverberg et a1. Dec. 9,1958 2,904,431 Moncriefi-Yeates Sept. 15, 1959 2,940,847 Kaprelian June14, 1960 2,987,660 Walkup June 6, 1961 3,010,883 Johnson et al. Nov. 28,1961 FOREIGN PATENTS 820,763 Great Britain Sept. 23, 1959 OTHERREFERENCES Perry: Chemical Engineers Handbook, McGraw- Hill, 1950; 3rded., pages 455-82 of interest.

Amick: RCA Review, December 1959, pages 753-769, 96-1FC.

Collins et al.: Physical Review, volume 112, No. 2, pages 388-395.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION atent Noo 3 154414 October 27 1964 Vsevolod Tnlagin et al,

It is hereby certified that error appears in the above numbered patantrequiring correction and that the said Letters Patent should read as:orrected below Column 3 lines -34 and 35 and lines 42 and 4L3 for "aphotoconductor electrolytically developable", each electrolyticallydevelopable occurrence, read a photoconductor same column 3 lines 38 and4L6 for "organic", each occurrence read inorganic column 4, for "carrierliquid with", each occurrence lines 5 and 13 read carrier with liquidSigned and sealed this 4th day of May 1965 SEAL) test:

EDWARD J. BRENNER RNEST W. SWIDER Commissioner of Patents testingOfficer

1. A PROCESS FOR RESTORING A PHOTOCONDUCTOR ELECTROLYTICALLY DEVELOPABLESHEET MATERIAL HAVING ONLY LATENT CONDUCTIVITY IMAGES THEREON TO ITSDARK ADAPTED STATE AND FOR WASHING THE SURFACE THEREOF WHICH COMPRISESCONTACTING AN ORGANIC PHOTOCONDUCTOR BONDED TO AN ELECTRICALLYCONDUCTIVE CARRIER WITH LIQUID WATER HEATED TO AT LEAST 100*F. ANDCOOLING THE HEATED PHOTOCONDUCTOR TO AMBIENT TEMPERATURE.